Art of cracking hydrocarbons



BY gm,

G. H. TABER, JR

Filed OGt. ll, 1928 May E2, 931.

ART oF CRACKING HYDRocARBoNs CTI Patented f E2, ESSE GEORGE H. TARE-R, JR., OF RYE, NEW YORK, ASSIGNOR TO SINCLAIR REFINING COM- PANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ART 0F CRACKING HYDROCARBONS Application led October 11, 1928. Serial No. 311,738.

This invention relates to improvements in operations carried out to produce lighter and lower boiling hydrocarbon oils, such as gasoline, from heavier and higher boiling hydrocarbon oils. such as kerosene, gas oil, fuel oil and the like, particularly by distillation under superatmospheric pressure. The invention is useful, however, in connection with other types of operations, such as those in which the oil to be cracked is heated to a cracking temperature in the vapor phase at either approximately atmospheric pressure or at higher pressures and processes in which the oil is heated to a cracking temperature, usually under very high pressures, without complete separation of vapors and unvaporized liquids in the cracking operation itself.

In certain aspects, this invention is an improvement upon the operation described and illustrated in United States Letters Patent No. 1,663,868, granted March 27, 1928, to the Sinclair Refining Company on my application.

In cracking operations in which the cracked products are taken olifI as a mixture of vapors and gases, either from the cracking operation itself or from some subsequent operation carried out to separate the lighter cracked products from residues the constituents of which are unsuitable as components of the desired product, the mixture usually includes vapors .of the desired lighter and lower boiling hydrocarbon oils, gases incondensable except under high pressures and at low temperatures, and constituents in gas or vapor form of an intermediate character. These intermediate constituents usually include bot-h saturated and unsaturated components. Hydrogen and 'methane may be mentioned as examples of the incondensable gases, and ethylene and the related unsaturated hydrocarbons as examples of the 'unsaturated intermediate constituents. In the usual condensing operation, a certain amount of the constituents suitable as components of t-he desired product are carried 0H uncondensed with the incondensable gases, and the diHicultly condensable intermediate constituents, or part of them, also escape in this same way. The recovery of the condensable constituents suitable as components of the desired product is of course desirable to improve the yield secured from the operation, and the appropriate return of the intermediate constituents, particularly the unsaturated components thereof, likewise assists in improving the eiciency and the yield secured in operation.

Hitherto it has been customary to subject such gas mixtures escaping from condensing operations employed in connection with cracking operations to a scrubbing operation with some absorbent medium from which the condensable hydrocarbons are subsequently separated and recovered, for example by distillation :trom the absorbent. Likewise, these gas mixtures have previously been subjected to scrubbing operations with raw stock to be supplied to the cracking operation so that absorbable constituents are separated and returned to the cracking operation whence they again escape with the gas and vapor mixtures including the desired product.

According to the present invention, the gas and vapor mixture remaining uncondensed, after the desired product has been condensed from the gas and vapor mixture from the cracking operation, is successively-subjected to two separate absorbent treatments with raw stock to be supplied to the cracking operation, the raw stock containing constituents absorbed in the irst absorbent treatment is passed in heat exchanging relation with hotl products escaping from the cracking operation on its way to the cracking operation and these absorbed constituents are, by this heat exchange, distilled from the raw stock without being subjected to the cracking operation proper, and the raw stock containing constituents absorbed in the second absorbent treatment is supplied to the cracking operation so that these absorbed constituents are, together with the stock supplied to the operation` subjected to the high temperatures prevailing in the cracking operation proper. In the rst absorbent treatment a predominance of the heavier more easily condensable constituents of the uncondensed gas and vapor mixture, such as are suitable as components of the desired product, are absorbed, and in the second absorbent treatment a predominance of the lighter less easily condensable constituents, such as the intermediate constituents previously mentioned, are absorbed. In this respect the process is largely selfregulating because heavier hydrocarbon constituents tend to displace lighter hydrocarbon constituents from the raw stock absorbent in the first absorbent treatment; this division of the absorbable constituents of the uncondensed gas and vapor mixture can, however, be controlled by regulating the relative rat-es at which raw stock is supplied to each of the two absorbent treatments. Thus, the constituents of the'uncondensed gas and vapor mixture suitable as components of the desired product are recovered in a particularly advantageous manner without danger of losses or formation of carbonaceous deposits within the cracking apparatus incident to subjection of such constituents to the cracking operation proper, and at the same time the lighter absorbable constituents of the uncondensed gas and vapor mixture are returned to the cracking operation proper in a particularly advantageous manner.

The invention will be further described in connection with the accompanying drawings, which diagrammatically illustrate one form of apparatus adapted for carrying out the process of the invention. Referring to the accompanying drawings, it will be appreciated that different types of apparatus lnay be employed to carry out the various steps effected in the apparatus shown, that the process is useful in connection with other types of cracking operations, and that a recovery system .such as that illustrated may be employed in connection with one or several cracking units.

The cracking still illustrated is of the general type described and illustrated in United States Letters Patent No. 1,285,200, granted November 19, 1918, to the Sinclair Refining Company on the application of Edward W.'

Isom. The still comprises a bulk supply tank 1 located away from a battery of vertical tubes 2 in a heating furnace 3, and connections 4, 5 and 6 and a circulating pump 7 for circulating oil from the bulk supply tank upwardly through the heat-ing tubes and back to the bulk supply tank.y Vapors and gases escape from the bulk supply tank through a reflux tower 8 from which gases and vapors remaining uncondensed escape through connection 9. For the production ofi gasoline or gasoline character distillates from gas oil or gas oil character charging stocks, stills of this type are operated under pressures up to to 125 pounds per square inch or somewhat higher and with lighter charging stocks, such as kerosene character oils, higher pressures up to 300 pounds per square inch or more are used.

The gases and vapors escaping through connection 9 are, in the apparatus illustrated, subjected first to a fractionating operation in the fractionating tower 10 and then to a refining operation in the refining tower 11. This fractionating operation may be controlled, for example, to produce directly a gasoline product of the desired boiling range so that the vapors escaping therefrom can be condensed, after being subjected to the refining operation, to produce directly a finished gasoline product. The fractionating tower 10, for example, may be a conventional bubble tower. Its operation may be controlled by the regulated reintroduction, through connection 12, of a part of the gasoline produc Heavier constituents condensed in the fractionating tower 10 are discharged through connection 13. In the relining operation carried out in tower 11, the gasoline vapors may be subjected, for eX- ample, to contact with an adsorptive catalyst such as fullers earth causing polymerization of constituents undesirable as components of the gasoline product. The apparatus illustrated has certain advantages in operation, but the fractionating tower 1() and the refining tower 11 are not essential in carrying out the present invention; the gases and vapors escaping through connection 9 may be immediately subjected to a condensing operation, in condenser 14 for example.

The gases and vapors from the cracking operation are subjected to condensation in the condenser 14. From this condenser, the condensate and the gases and vapors remaining uncondensed are discharged into a receiver 15 where the condensate and the gas and vapor mixture separate. The pressure on the still system may be regulated and reduced by Valves between the still and the condenser, by means of valves 16 or 17 for example, or by valves beyond the condenser. Where the condensation is carried out under pressure and the condensate is initially collected Linder pressure, it is sometimes advantageous to discharge the condensate into another receiver in which the pressure is reduced and from which any liberated gases and vapors are conducted together with the gas and vapor mixture remaining uncondensed under pressure to further treatment.

, Similarly, gases and vapors separating from the condensed product, in storage for example, may with advantage be subjected to further treatment together with the gas and vapor mixture from the condensing operation (as by the blower 18 in the apparatus illustrated). From the receiver 15, the uncondensed gases and vapors escape throughconnection 19.

This gas and vapor mixture is passed first through scrubbing tower 21 and then through scrubbing tower 22, escaping through connection 20. The connections are arranged for introducing the gas and vapor mixture at the bottom of the scrubbing towers and exhausting it from the upper ends of the scrubbing towers. These scrubbing towers may be of This raw stock may be supplied to the two absorbent treatments from a common source lor from separate sources, as in the apparatus illustrated.

The raw stock containing constituents absorbed in the first scrubbing tower 21 is introduced, through connections 25 and 26 by means of pump 27, into t-he upper end ot' the reflux tower 8 in direct contact with the vapors therein. In the reflux tower 8, the absorbed constituents are vaporized from the raw stock supplied from the first scrubbing tower by heat exchange with the hot vapors from the still to escape with the gases and vapors remaining uncondensed from the reflux tower through connection 9 to be condensed as part of the cracked product in the condenser 14. lhile ample heat is available in the reflux tower 8 to effect this distillation of these absorbed constituents, the temperatures to which the absorbed constituents are thus subjected are low enough so that objectionable overcracking of these absorbed constituents is avoided. The remaining unvaporized raw stock from which these absorbed constituents have thus beenstripped is then supplied, with the reflux condensate, from the reiiux tower to the cracking still proper through connection 28.

The raw stock containing constituents absorbed in the second scrubbing tower 22 is introduced into the cracking still proper, through connections 29 and 30 by means of pump 35, so that these absorbed constituents are compelled to pass with the stock through the zone of maximum temperature in the cracking still proper. In the cracking still illustrated, these absorbed constituents, in troduccd into the circulating still charge through the bearings odc-he circulating pump 7, are compelled to pass upwardly through the heating tubes 2 while intimately distributed through the circulating still charge, the latter including raw stock and reflux condensate. In cracking stills in which unvaporized oil is not recirculated through the heating zone, these absorbed constituents may similarly be compelled to pass through the zone of maximum temperature by forcing the raw stock containing these absorbed constituents through the heating zone either with or without other admixed raw stock or either with or without admixed reflux condensate.

The circulating pump forming part of the cracking still illustrated is of the general type described and illustrated in United States Letters Patent No. 1,676,202 and No. 1,676,203 granted July 3, 1928, to the Sinclair Refining Company on the applications of Edward W. Isom and John E. Bell. Stock tanks 31 and 32 are shown floating on the charging stock lilies between the first scrubbing tower and the reflux tower and between the second scrubbing tower and the cracking still proper and by-passes 33 and 34 are provided to permit independent regulation andcontrol of the scrubbing operations and the cracking operation.

Polymers or other boiling material sep; arated from the vapors condensed to form the cracked product in the refining operation, if one is used, may be returned to the cracking operation either with the raw stock from the iirst absorbent treatment or with the raw stock from the second absorbent treatment. In the apparatus illustrated, V such polymers or other oily material, discharged from the refining tower 11 through connection 36, may be supplied in whole or in part to the'stock tank 31 or in whole or in part'- to the stock tank 32 or may be discharged in whole or in part to storage.

As previously mentioned, a recovery system such as that illustrated may be employed in connection with one or several cracking units. For example, a number of cracking stills of the type illustrated may be connected to the recovery system through connections 37, 38 and 39 just as the cracking still illustrated is connected.

Where the invention is practiced in connection with'pressure distillation operations. 'a part of the still pressure may be employed to Jforce the gas and vapor mixture through the scrubbing towers. The pressure, for example, may be reduced at a point either between the cracking still Aand the condenser or beyond the condenser to a value suciently above atmospheric pressure to e'ect this end. The circulation of the gas and vapor mixture through the scrubbing towers may, however, be effected by blowers or the gas and Vapor mixture may be drawn through the scrubbing towers by means of an exhauster.

In carrying out the invention in the apparatus illustrated, the gas and vapor mixture remaining uncondensed from the condenser 14 is subjected successively to a first absorbent treatment in the scrubbing tower 21 and then to a second absorbent treatment in the scrubbing tower 22, raw stock supplied to the irst absorbent treatment as an absorbent is supplied from the scrubbing tower 21 to the reflux tower 8 and introduced into direct contact with the 'vapors in the reiiux tower and raw stock supplied to the second absorbent treatment as an absorbent is supplied from the scrubbing tower 22 to the cracking still proper so that this raw stock containing the constituents absorbed in the second absorbing.

' forming some similar fraction. For example,

the distillation of the constituents absorbed in the lirst absorbent treatment from the raw stock there used as an absorbent may be effected by heat exchange with a residue discharged hot from the cracking still or a vaporized fraction of this residue.

I claim;

l. In cracking operations for the production of lighter hydrocarbon oils from heavier hydrocarbon oils in which vapors and gases are taken oit and subjected toA a condensing operation, the improvement which comprises subjecting the ygas and vapor mixture remaining uncondensed thereafter successively to a first absorbent treatment with raw stock subsequently supplied to the crackin@ operation and then to a second absorbent treatment with raw stock subsequently supplied to the cracking operation, subjecting the vapors taken oil.P from the cracking operation to a retluXing operation before subjecting them to the irst mentioned condensing operation and introducing the raw stock containing constituents absorbed in the first absorbent treatment into direct contact with the vapors therein, supplying reiiuX condensate and unvaporized raw stock from this refluxing operation to the cracking operation proper, and supplyingI the raw stock containing constituents absorbed in the second absorbent treatment to the cracking operation so that these absorbed constituents must pass with the stock directly to the zone of maximum temperature in the cracking operation proper.

2. In cracking operations for the production of lighter hydrocarbon oils from heavier hydrocarbon oils in which vapors and gases are taken off and subjected to a condensing operation, the improvement which comprises subjecting the gas and vapor mixture remaining uncondensed thereafter successively to a lirst absorbent treatment with raw stock sub- Lacalle sequently supplied to the cracking operation and then to a second absorbent treatment with raw stock subsequently supplied to the cracking operation, distilling absorbed constituents from the raw stock from the first absorbent treatment by heat exchange with hot products escaping from the cracking operation and then supplying this raw stock to the cracking operation proper and supplying the raw stock containing constituents absorbed in the second absorbent treatment to the cracking operation so that these absorbed constituents must pass with the stock directly to the zone of maximum temperature in the cracking operation proper.

In testimony whereof I affix my signature.

GEORGE H. TABER, JR. 

